CLAMPING DEVICE

Abstract: A clamping device for sheetlike objects (2), such as a photosensitive film or plates with a photosensitive layer, onto a rotary arranged, preferably cylindrical drums (11) mantle surface (3) by fixing one edge portion (6) of an object. The device is especially characterized by a clamping device (4) equipped with clamping fittings (12, 14) adapted to clamp an edge portion (6) of an object (2) and to prevail in a non activated state by means of a spring force pressed down onto the drum (1) and thereby connecting with and providing one portion of the drum mantle surface (3) and to prevail in a clamping position against said spring force partly raised from the drum, by means of a force (F) preferably applied from the outside of the drum to clamp, by means of the clamping fittings, the object adapted to be hold by means of the clamping fittings by a spring force.

Description: Clamping Device The present invention relates to a device to clamp sheetlike objects in the form of principially a film or plates onto a rota¬ ry arranged, preferably cylindrical drum by fixing one edge por¬ tion of the object. According to one way to expose photosensitive objects, such as film or plates for offset printing the object is placed on a rotary arranged drum with its photosensitive layer facing out¬ wards and is illuminated and thereby exposed at certain spots by one or several light sources with the drum rotating so that a desired pattern consisting of spots is achieved. Then the preci¬ sion regarding the object position on the drum must be maintained on an extremely high level, the printing to be performed by means of or via the object being composed of prints from several ob¬ jects. Different colours are thus achieved by printing prime colours implying spots coming from several objects to be overlap¬ ped with a very high precision to achieve a right colour without any shades in the colour field. Therefore high demands do exist for the clamping devices for the object. In a non activated state a surface in perfect alig¬ nment with the drum has to be avaiable. Moreover, no holes/gaps should exist, if not of a very small magnitude, for not letting the object be sucked from its place on said outer surface by the suction from inside which is used to keep the object in place on the outside. In an activated state the object has to be held in such a way that large forces can be allowed on the object in the tangential drum direction without displacing the object. In a radial or similar direction, however, comparably moderate forces should hold the object in place to prevent damages of it. Fur¬ thermore, the object shall be hold in said desired way inspite of that the drum rotates with a very high speed, e.g. 1300 rpm. Moreover, the clamping device should in an activated state prot¬ rude very little from outside the drum to prevent any undesired air current phenomena in connection with the drum. Another secon¬ dary demand implies a multitude of clamping devices to be present and that during the clamping of the object some of these are ac¬ tivated and some non activated and then are covered by an object. The present invention relates to clamping devices fullfil- ling these very strongly put demands and which, moreover, have few parts and are comparably cheep in production. Thus the inven¬ tion relates to a clamping device according to the first part of the attached claim 1. The device is characterized especially by the characterizing part of said claim. The invention is described in detail in connection with embodiments and the attached dra¬ wings, where - fiure 1 is a top view of a first embodiment of a clamping devi¬ ce of the invention in a non activated state and here against the drum outside, on which it is placed, - figure 2 is a bottom view in figure 1 of the device of figure 1, - figure 3 is a view of the device of figure 2 in an activated state holding an object protruding to the left, - figure 4 is a view of the device of figure 2 in a clamped state preceding the state in figure 3, and - figurer 5-8 are views of another embodiment of a device of the invention corresponding to figures 1-4. In figure 1 a rotary adapted, preferably cylindric drum is designated by 1, on which sheetlike objects 2, such as a photo¬ sensitive film 2 or plates 2 with a photosensitive layer are in¬ tended to be fixed onto the drum mantle surface 3. A clamping device is designated by 4, being equipped with clamping fittings 5 and thus arranged to clamp an edge portion 6 of an object 2 to fix the object, the object being simultaneously adapted to be hold, e.g. at its edge portion (not shown) facing said edge portion 6. The clamping device 4 is arranged and adapted to be hold in a non activated state, figures 1 and 2, onto an indentation 7 of the drum debouching at the mantle surface and thereby connecting with and providing a portion of the drum mantle surface, the in¬ dentation form at the mantle surface preferably coinciding as much as possible with the clamping device profile at the mantle surface so that only a comparably little gap 8, figure 1, pre¬ vails around the clamping device at the mantle surface. Furthermore, the clamping device is adapted to prevail in a clamping situation, figure 3 and 4, partly raised or similar from the drum against said spring force by means of a spring force F, figure 4, acting from the outside of the drum, to be clamped by means of the clamping fittings, the clamping device being adapted to hold the object by a spring force acting via the clamping fit¬ tings. According to a prefered embodiment the clamping device com¬ prises a lever portion 10 articulated around a beneath and sub¬ stantially parallell to the mantle surface running axis of rota¬ tion 9 and comprises the clamping device portion 11 adapted for a connection with the mantle surface and an outer clamping lever 12 adapted to provide in said non activated state a portion of the connection 11 with the mantle surface and a weight portion 13, the outer clamping lever and the weight portion then being ar¬ ranged on different sides of the rotation axis 9. The outer clamping lever is adapted to clampingly cooperate with an inner clamping lever 14, the levers 12, 14 then being ar¬ ranged mutually pivotable, revolving on the axis of rotation to be set off from each other by a spring force to adapt a clamping position, shown in figure 4. Preferably the clamping device is adapted to be kept in place by a first spring force, here created by a first torsion spring 15, and the clamping levers are adapted to be set off against each other by another spring force, here created by a second torsion spring 16, the second spring force being the one holding the object by means of the clamping fit¬ tings having clamping levers 12, 14, according to figure 3. In the first embodiment the levers 12, 14 are simultaneously articu¬ lated by pivoting the clamping device. Preferably said second spring force is larger than said first spring force. In the second embodiment the lever portion 10 is arranged in generally the same way as in the first embodiment, the outer clamping lever 12, however, being adapted to clampingly cooperate with an inner bucker 17 movable to and from the mantle surface and adapted during clamping to be pressed against the outer clam¬ ping lever by said spring force, being preferably created by a compression spring 18, while said first spring force is created by a torsion spring 19 as previously. Said bucker, preferably comprising a movable pin 20 adapted to contact an object, is thus adapted to be moved towards the drum inside against said spring force. In both embodiments the clamping device is preferably adap¬ ted to pivote from a non activated position, before reaching the clamping position, the object being adapted to be kept clamped by said second spring force and pressed down against the mantle sur¬ face by said first spring force as shown in figures 3 and 7. As previously mentioned, the clamping device is preferably equipped with a weight portion adapted to supply a force by cent¬ rifugal action during the rotation of the drum, this force trying to return the clamping device to said non activated position. The operation of the clamping device of the invention is generally demonstraed above. Thus, the clamping device is in its non activated position kept pressed into the indentation and in connection with the mantle surface. The clamping position is achieved by means of a force supplied from outside, this being essentially easier than an action from inside the drum, and the outer clamping lever can be raised passing an object edge in level with the mantle surface to clamp the object later on in cooperation with the inner clamping lever/bucker, the clamping device reaching a low profile position, where the object is pres¬ sed against the mantle surface by said first spring force. In using two spring forces the clamping forces and holding-down for¬ ces can be adapted individually. Being obvious from the above, the invention provides most essential advantages and fullfills the highly put demands reques¬ ted i.a. by an application to printing purposes. The invention has been described above in connection with embodiments. Further embodiments and minor changes and amplifica¬ tions are of course possible without deferring from the spirit of the invention. Thus, different end buckers S are shown in the drawings, their function being evident. The indentation for the clamping device and thus for the clamping device portion connecting with the mantle surface need not to have a square profile and a variety of other profiles are possible. Furthermore, other types of springs, such as rubber springs, tension springs, etc. can be used. As previously demonstrated the raising or similar of the clamping device from the drum is preferably adapted to be perfor¬ med by a force acting from the outside of the drum and in direc¬ tion towards the drum. Also embodiments are possible, where a force acting from the inside is used and is achieved by means of devices placed beneath the drum mantle surface, such as pneumati¬ cally operated devices. It is essential that the drum mantle surface, at least for the application here described for printing purposes, remains substantially continuous and intact, a narrow gap existing be¬ tween the mantle surface and the clamping device. The invention is thus regarded not to be limited to the em¬ bodiments shown above and can be varied within the scope provided by the attached claims.

Claims: Claims 1. A clamping device for sheetlike objects such as a photo¬ sensitive film or plates with a photosensitive layer onto a rota¬ ry adapted, preferably cylindrical drums mantle surface by fixing one edge portion of the object, characterized by a clamping devi¬ ce (4) equipped with clamping fittings (12, 14, 17) adapted to clamp an edge portion (6) of an object (2) and to prevail in a non activated state by means of a spring force pressed down onto the drum (1 ) and thereby connecting with and providing one por¬ tion of the drum mantle surface (3) and to prevail in a clamping position against said spring force partly raised from the drum, by means of a force (F) preferably applied from the outside of the drum to clamp by means of the clamping fittings, the object adapted to be hold by means of the clamping fittings by a spring force. 2. A device according to claim 1, characterized in that the clamping device is adapted to be kept down by a first spring force and by means of the clamping fittings holding the object by a second spring force. 3. A device according to claim 1 or 2, characterized in that the clamping device is pivotable around a rotation axis (9) run¬ ning beneath said mantle surface, the clamping fittings and the weight portion (13) of the clamping device being arranged on dif¬ ferent sides of the axis, perpendicular with it. 4. A device according to claim 1, 2 or 3, characterized in that the clamping device comprises an outer clamping lever ( 12) adapted to provide a portion of the connection (11) with the mantle surface in a non activated state. 5. A device according to claim 4, characterized in that said outer clamping is adapted to clampingly cooperate with an inner clamping lever (14), the levers being mutually pivotably arranged to be set off against each other by said spring force to reach a clamping position. 6. A device according to claim 5, characterized in that the levers (12, 14) are simultaneously pivotable by swivelling the clamping device. 7. A device according to claim 5 or 6, characterized in that said second spring force is larger than said first spring force. 8. A device according to claim 4, characterized in that said outer clamping lever (12) is adapted to clampingly cooperate with an inner bucker (17) movable to and from the mantle surface and during clamping being adapted to be pressed against the outer clamping lever by said second spring force. 9. A device according to claim 8, characterized in that said bucker preferably comprising a movable pin (20) , is adapted to be moved towards the inside of the drum against said second spring force. 10. A device according to claim 5, 6, 7 and 9, characterized in that the clamping device is adapted to swivel from its non ac¬ tivated state before reaching the clamping position, the object being adapted to be firmly held by said second spring force and kept down onto the mantle surface by said first spring force. 11. A device according to anyone of the proceeding claims, characterized in that the clamping device is equipped with a weight portion ( 13) adapted to provide a force during the rota¬ tion of the drum, the force attempting to return the clamping fittings to said non activated position. 12. A device according to anyone of the proceeding claims, characterized in that the clamping fittings are arranged in an indentation (7) debouching at the drum mantle surface with a cer¬ tain profile at the mantle surface, the profile nearly coinciding with the clamping device profile in connection with the mantle surface so that only a little gap is provided around the clamping device.

Inventors: NIEMI ERIK, NIEMI, ERIK
Applicants: MISOMEX AB, NIEMI ERIK, NIEMI, ERIK
Application year: 1994
Main classification: B41F27
IPC codes: B65H5, G03F7